Erosion resistant composites

ABSTRACT

Erosion and wear resistant metal composites are disclosed that comprise a metal alloy substrate and a coating composition bonded to said substrate; the coating composition consisting essentially of nickel, chromium, boron, silicon and titanium carbide in the following percentages by weight of the coating composition: NICKEL 14% TO 80% CHROMIUM 0.5% TO 10% BORON 0.2% TO 5% SILICON 0.3% TO 8% TITANIUM CARBIDE 6% TO 82% A process is disclosed for producing the composites wherein a first coating containing all of the foregoing metals are applied via a slurry coating technique followed by drying, heating and pressing steps and thereafter a second slurry coating step is used wherein the metal ingredients of nickel, chromium, boron and silicon are applied followed by drying and heating steps.

United States Patent 1 1 Reznik 1111 3,847,559 1451 Nov. 12, 1974 1EROSION RESISTANT COMPOSITES Barry David Reznik, Brooklyn, NY.

[73] Assignee: DeWiant Corporation, Detroit,

Mich.

122] Filed: May 28, 1969 [21] Appl. No.: 828,702

[75] Inventor:

[52] US. Cl 29/195, 29/182.8, 29/195 [51] Int. Cl B32b 15/00 [58] Fieldof Search 29/195, 196, 196.1, 196.6,

Primary ExaminerI-lyland Bizot [57] ABSTRACT Erosion and wear resistantmetal composites are disclosed that comprise a metal alloy substrate anda coating composition bonded to said substrate; the

- coating composition consisting essentially of nickel,

chromium, boron, silicon and titanium carbide in the followingpercentages by weight of the coating composition:

nickel Y [4'71 to 8071 chromium 0.571 to 10% boron 0.29110 5% silicon0.3% to 8% titanium carbide 6% to 8271 'A process is disclosed forproducing the composites wherein a first coating containing all of theforegoing metals are applied via a slurry coating technique followed bydrying, heating and pressing steps and thereafter a second slurrycoatingstep is used wherein the metal ingredients of nickel, chromium,boron and silicon are applied followed by drying and heatingsteps. 7

7 Claims, N0 Drawings BACKGROUND OF THE INVENTION 7 This inventionrelates to erosion and wear resistant metal composites. Morespecifically it-relates to metal composites that are particularly wellsuited for the fabrication of compressor blades and other jet engineparts that are subjected to erosion and wear by solids, generally in theform of dust. As is known, the replacement costs resulting from dusterosion of military and commercial gas turbine engines are excessive.

Erosion resistant parts fabricated from alloys such as 41088, AM350 andIN718 can be made by providing a coating composition over the'alloysubstrate via the chemical vapor deposition of titanium carbide.Although this process provides parts having excellent erosionresistance, it isa difficult and costly process.

It is also known that the erosion resistance of various materials dependupon several factors, among which are the physical characteristics ofthe material and the angle of impact of'the solids. For example, maximumerosion of ductile materials occurs when the impact angle is about andfor brittle materials an impact angle of about 90 causes the maximumerosion.

It is believed, therefore, that a composite that will resist erosionregardless of the angle of impact of the solidsand is relatively easy toproduce with excellentreproducibility would be an advancement in theart.

SUMMARY OF THE INVENTION In accordance with one aspect of thisinvention, there is provided a metal composite comprising an alloysubstrate, as a major component and bonded to the substrate an erosionresistant coating composition consisting essentially of the followingmaterials in percentages by weight:

nickel 14% to 80% chromium 0.5% to 10% boron 0.2% to 5% silicon 0.3% to8% titanium carbide 6% to 82% In accordance with another aspect of thisinvention, there is provided a process forfproducing said metalcomposite. The process comprises (a) applying to a clean alloysubstratea first coating of a slurry comprising a powdered metal material, afugitive binder and a fugitive solvent for the binder; the powderedmetal material consisting essentially of the following'ingredients inpercentages by weight of the total metal material:

nickel 6.5% to 30% chromium 0.5% to 3.5% boron 0.2% to 2.0%. silicon I0.3% to 2.5%. titanium carbide 67% to 91% centages by weight of thetotal second powdered metal material:

nickel 75% to 90% chromium 4.6% to 11.5% boron 2.2% to 5.5% silicon 3.2%to 8.0%

' together with other and further objects, advantages and capabilitiesthereof, reference is made to the following a disclosure and appendedclaims in connection with the above description of some of the aspectsof this invention. a

I DESCRIPTION OF THE PREFERRED EMBODIMENTS In general, the composites'ofthis invention are produced by use of the slurry technique of applyingcoatings. The slurries used comprise a powdered metal material, avolatile or fugitive binder and a volatile or fugitive solvent for thebinder. These methods are well known in the art and are used forapplying metal coatings by spraying, dipping or brushing of the slurryonto the substrate followed by a drying and heating step whereinessentially all of the binder and solvent are removed and the metalmaterial adheres to the substrate. The types of suitable binders andsolvents are known to one skilled in the art of coating compositions. 4

The metal powders are thoroughly mixed together in a suitable blender ormixing device (e.g. a V v I blender) untila substantially homogeneouscomposition has been obtained. A similar procedure is followed if amixture of different alloys or of elemental metal (or metalloid) and ofalloyed material is employed.

The powdered metal is converted into a liquid coating composition,adapted for application (e.g. by dipping, brushing, spraying or thelike) to the superalloy substrate, by suspending it in a suitablevehicle, e.g., a solvent solution of temporary or fugitive binder whichcan be a natural or synthetic binder.

Examples of fugitive binders that can be employed are solvent solutionsor dispersions of the various available synthetic polymers, such aspolyacrylamide, polyvinyl acetateand the homopolymers and copolymers ofthe lower alkyl (e.g. C through C acrylates and methacrylates with eachother and with other compounds containing a monoethylenicallyunsaturated grouping. It is preferred to employ anordinary-nitrocellulose (pyroxylin) lacquerwherein the solvent is, forexample,

acetone.

The concentration of the powdered metal in the vehicle and the amount ofsolvent in the same are varied as desired, depending upon such factorssuch as'the particular method of applying the coating (brushing,spraying or dipping), the desired thickness of the individual coating,the number of coatings to be applied, the viscosity of the vehicle, thedesired covering power .of the coating composition, and otherinfluencing factors. Typically, the metal powder is present in thecoating'composition in an amount corresponding to about 1,500 to about3,000 grams per 1 ,000 gms. of the -vehi- I I v I The powders are mixedwith the vehicle by mechanical stirring. Any suitable mixer can be used,however, mixers of the type generally employed in mixing paints arepreferred for this purpose. Mixing is continued at any suitabletemperature for a time sufficient to provide a substantially homogeneouscomposition. The titanium carbide and the nickel, chromium, silicon andboron are generally incorporated into the slurry in the form of a finelydivided powder having essentially all of the particles of the powderedmetal smaller than the openings in a 325 mesh screen (US. Sieve). Thetitanium carbide and the other ingredients can be added to the slurryindividually or can be added separately as long as the final slurry hasthe proper amounts of desired metals relatively uniformly distributedthroughout the slurry. Any suitable mixer can be used to provide therelatively uniform slurry such as those normally used for mixing paints.

Although the amount of nickel, chromium, boron and silicon can be variedwithin the ranges heretofore given, it is preferred to use a'nickel basealloy braze consisting essentially of about 86% nickel, about 6.5%chromium, about 3% boron and about 4.5% silicon to provide a ductilematrix for the titanium carbide. The weight ratio of the foregoing alloybrazes to the titanium carbide can be varied from about 1:10 to about1:2 with satisfactory results. A weight ratio of nickel base alloy totitanium carbide of from about 1:4 to about 1:6 is preferred.

After the first slurry coating is applied and thereafter dried, thecoated material is heat treated at a temperature of from about 1,750F toabout 1,900F for a relatively short period of time, generally less thanabout one hour. Although-the temperature can be varied between about1,750F and 1,900F and some of the ben-,

efits of the invention can be achieved, it is preferred to use atemperature of from about 1,830F to about 1,850F, low temperatures tendto not sufficiently wet the titanium carbide particles and the highertempera tures can have some undesirable effects upon the properties ofthe substrate particularly if the temperature is maintained near theupper limit for prolonged periods,

such as over an hour. Thereafter, the coated material is isostaticallypressed to increase the density of the first coating. Generally, thepressures used are from about 10,000 'psi to about 40,000 psi. It hasbeen found that pressures of from about 15,000 psi to about 25,000 psiyield densities that arepreferred. .In order to compact the firstcoating it is necessary to'enclose the coated substrate in a relativelythin filmof a relatively impervious material such as a polyethyleneplastic film. An example of such a material is Visten film manufacturedby Union Carbide Corporation.

After the isostatic'pressing step, the coated material is coated with asecond slurry. Although in most instances, for ease of operation, aslurry that is essentially the same as the slurry used for the firstcoating but without the titanium carbide, will be 'used for the secondcoating. The second coating can be varied within the specified amountsof ingredients, therefore, the second slurrycan contain powdered metalmaterials in the following ranges:

nickel 75% to 90% silicon As can be appreciated, the same or differentformulations can be used for the first or second coatings with theexception of the addition of titanium carbide in the first coating andabsence thereof in the second coating. However, use of the sameformulation is preferred. The second coating infiltrates the relativelyporous first coat thus yielding excellent strength and appearance to thecoated substrate. After the second coating has been applied the coatedsubstrate is dried and heated to a temperature of from at least about1,780F to about 1,900F and preferably from about 1,830F to about 1,850Ffor at least about 10 minutes.

The overall thickness of the coating can be varied. A coating having athickness at least about 3 mils is needed to provide appreciableresistance to erosion. In general, as the thickness of the coating isincreased, the

lifetime of the'composite is increased. In most instances however, froman economic standpoint and because adherence of large thicknesses ofcoatings is difficult, the overall thickness of coating greater thanabout 15 mils will not be used.

It is to be noted that although two separate coating applications areused, there are not two distinct layers. Photomicrographs of a crosssection of the metal composite indicates a relatively complete diffusionof the ingredients of the coating and some diffusion between thesubstrate and the coating. In some instances the titanium carbideparticles are relatively more concentrated at the center of the coatingand with the nickel alloy matrix being relatively more concentrated atthe surface and interface;

The ratio of thickness betweenthe first and second coating applicationscan be varied. In most instances, the ratio of first coating thicknessto second coating thickness will be from about 1:9 to about 9:1 with arange of from about 1:5 to about 5:1 being preferred. In the process ofthe present invention it is onlynecessary to vary the weight ratios ofthe slurry application to achieve the beforementioned ratios.

It is believed that the combination of the ductile and brittle materialsthat comprise the coating composition of this invention offer theadvantages of being resistant to erosion regardless of the angle ofimpact of the solids. As was previously mentioned, the angle of maximumerosion for ductile materials is about 20, therefore, even though theductile nickel base alloy erodes at surfaces that are subjected to theseangles, the titanium carbide particles being hard and brittle willresist erosion. At higher angles, such as about 90 the nickel alloymatrix'will offer its largest resistance where the attack on the brittletitanium carbide is the greatest. The choice of the level of theparticularingredients, that is titanium carbide and nickel alloy, willdepend to a large degree upon the particular use and the impact anglesof a majority of the particles causing the erosion.

coating compositions have the following ranges of in-.

gredients in percentages by weight:

nickel chromium 3% to 7% boron 1% to 3% silicon 2% to 5% titaniumcarbide 15% to 45% Although cemented carbides are the closeststructurally tothe type of coatings used for the metal composites ofthis invention, the processing temperature for producing the cementedcarbide coatings is about 3,000F which is above the melting point ofmany of the alloys that can advantageously be employed in the compositesof this invention.

Alloys that can be utilized as substrate in the practice of thisinvention include stainless steels, nickel or cobalt based superalloysor other alloys thermally stable at the processing temperatures used inthe practice of this invention, that is alloys that are thermally stableat I temperatures above 1,750F. Other alloys will be suggested to oneskilled in the art reading the disclosure contained herein.

When some alloys are used as substrates, the bond of the coatings to thesubstrate can be even further improved by incorporating relatively smallamounts of silver as one of the ingredients ofthe coating. In mostinstances, the amount of silver is greater than about 0.1 percent byweight of the total metal in the coating.

Larger amounts such as S-percent can be used, however, addition of largeamounts of silver add to the cost of the coating without derivingcorresponding benefits, therefore, when silver addition is used theamounts will generally be from about 1% to about 3% by weight of thetotal amount of powdered metal in the coating composition.

To more fully illustrate certain aspects of this invention, thefollowing detailed examples are given. All

parts, proportions and percentages are by weight unless designatedotherwise.

EXAMPLE I A slurry is prepared by mixing about 80 parts of titaniumcarbide having essentially all of its particles smaller than the openingin a 325 mesh screen (U.S. Sieve) and about 20 parts of a finely dividednickel base alloy ('Ni6.5Cr4.5Si-3B) with about 40 partsless steel typealloy by spraying with a conventional paint sprayer. Sufficient slurryis used to yield a thickness of about 3 to 4 mils after the coating isair-dried to remove most of the solvent. After air drying,"the coatedarticle is heated by radiant heating in a furnace at l,8-F in avacuumfor about 15 minutes.

After the material is cooled to room temperature, it is sealed inVisten' plastic film bags manufactured by Union Carbide andhydrostatically pressed at a pressure of about 20,000 psi for aboutZminutes.

After the isostatic pressing step the plastic film is removed and asecond coating using the same slurry, except that no titanium carbide isused, is applied to yield an'overall coating thickness after air dryingof about 6-8 mils. Heating at about 1,850F for about 15 to 30 minutesproduces a composite havinga 410SS substrate coated with a metalcomposition containing about 27% titanium carbide, about 4.8% chromium,about 3.3% silicon, about 2.2%-boron and about 62.7% nickel. I

Samples of the composite prepared above and uncoated 41088 are testedforerosion by usinga conventional grit blaster, using Pangborn 6120 irongrit at 40. I

psi feed pressure and at a nozzle distance of 5 inches. Results of theerosion tests are given in Table I below.

The above tests illustrate the superiority'of erosion resistant of thecomposite of this invention as compared to uncoated 410SS.

EXAMPLE II Using a process substantially similar to that employed inExample l, substrates of IN718 and AM,350 are coated and tested as inExamplel, for 5 minutes of erosion. Results of the erosion tests are asfollows:

TABLE II LOSS (mils) Coated composite Uncoated IN 718 2.1 10 AM 350 .1.210

The above results indicate the appreciable protection given by thecoating compositions of the present invention. Similar results areachieved when the amounts of titanium carbide are varied within thelimits disclosed.

While there has been shown and described what is at present consideredthe preferred embodiments of the invention, it will be obviousto thoseskilled in the art I that various changes and modifications may be madetherein without departing from the scope of the invention as defined bythe appended claims.

I claim: v 1. An erosion resistant metal composite comprising an alloysubstrate as its principal component and a coating composition bonded tosaid substrate, said coating consisting essentiallyof nickel, chromium,bo ron, silicon and titanium carbide in the following percentages byweights of said coating composition:

nickel I 14% to 80% chromium 0 5% to 10% boron 02% to 5% silicon 0.3% to8% titanium carbide 6% to 82% said composite exhibiting erosionresistance at substantially all angles-of impact of solids.

2. A composite according to 'claim l wherein said coating contains 'thefollowing ingredients in percentages by weight:

nickel- 50% to chromium 3% to 7% boron 1% to 3% silicon 2% to 5%titanium carbide 3. A composite according to claim 2 wherein said 4. Acomposite according .to claim 2 wherein said coating contains thefollowing ingredients in percent- Substrate i a Stainless steel ll agesby weight: 5. A composite according to claim 2 wherein said substrate isa nickel based superalloy. flicker 67.5% 6. A composite according toclaim 3 wherein said E22? substrate is a cobalt based superalloy.Silicon 33% 7. A composite according to claim 2 wherein said titaniumcarbide 27% v coating composition contains from about 0.1 to about andwherein said substrate is a type 410 stainless steel 10 5 P y weight ofSilver-

1. AN EROSION RESISTANT METAL COMPOSITE COMPRISING AN ALLOY SUBSTRATE ASITS PRINCIPAL COMPONENT AND A COATING COMPOSITION BOUNDED TO SAIDSUBSTRATE, SAID COATING CONSISTING ESSENTIALLY OF NICKEL, CHROMIUM,BORON, SILICON AND TITANIUM CARBIDE IN THE FOLLOWING PERCENTAGES BYWEIGHTS OF SAID COATING COMPOSITION:
 2. A composite according to claim 1wherein said coating contains the following ingredients in percentagesby weight:
 3. A composite according to claim 2 wherein said coatingcontains the following ingredients in percentages by weight:
 4. Acomposite according to claim 2 wherein said substrate is a stainlesssteel alloy.
 5. A composite according to claim 2 wherein said substrateis a nickel based superalloy.
 6. A composite according to claim 3wherein said substrate is a cobalt based superalloy.
 7. A compositeaccording to claim 2 wherein said coating composition contains fromabout 0.1 to about 5 percent by weight of silver.